make context options available to renderer

src/ol/source/Tile.js

@@ -167,6 +167,13 @@ class TileSource extends Source {
     return covered;
   }
 
+  /**
+   * @return {Object|undefined} Context options.
+   */
+  getContextOptions() {
+    return undefined;
+  }
+
   /**
    * @param {import("../proj/Projection.js").default} projection Projection.
    * @return {number} Gutter.